A typical prior art head and disk system is illustrated in FIG. 1. In operation the head 10 is supported by the suspension 13 as it flies above the disk 16. The magnetic transducer, usually called a “head,” is composed of elements that perform the task of writing magnetic transitions (the write head 23) and reading the magnetic transitions (the read head 12). The electrical signals to and from the read and write heads 12, 23 travel along conductive paths (leads) 14 which are attached to or embedded in the suspension 13. Typically there are two electrical contact pads (not shown) each for the read and write heads 12, 23. Wires or leads 14 are connected to these pads and routed in the suspension 13 to the arm electronics (not shown). The disk 16 is attached to a spindle 18 that is driven by a spindle motor 24 to rotate the disk 16. The disk 16 comprises a substrate 26 on which a plurality of thin films 21 are deposited. The thin films 21 include ferromagnetic material in which the write head 23 records the magnetic transitions in which information is encoded.
There are several types of read heads 12 including Giant Magnetoresistive (GMR) and tunnel junction. It is important for the two leads (not shown) that provide the electrical connection to the sensor element (not shown) in a magnetoresistive head 12 to be of low resistance, to be consistently manufacturable and to be resistant to formation of shorts during the manufacturing process. Typically leads (not shown) have been made from copper, tungsten, tantalum or gold, but the requirements of heads like spin valves make these traditional simple leads inadequate. To meet the new requirements, leads with a multilayer structure have been proposed. For example, U.S. Pat. No. 5,438,470 to Ravipati, et al., suggest using a thin layer of tantalum under a layer of gold for the leads. Ravipati '470 also teaches that lower resistance leads are obtained by placing the leads in contact with the hard bias layer as well the magnetoresistive sensor. U.S. Pat. No. 5,491,600 to Chen, et al., describes leads with two refractory metal layers sandwiching a highly conductive metal layer. One embodiment is alternating layers of tantalum and gold. In the particular type of head described in Chen '600, the leads from the spin valve sensor layer stack are formed on material used for the hard bias, e.g., CoPtCr. The CoPtCr layer in turn has a Cr underlayer.
U.S. Pat. No. 5,883,764 to Pinarbasi similarly describes a multilayer lead structure, for example, 3.5 nm Ta, 3.5 nm Cr and 75 nm Ta. The hard bias layer is again CoPtCr.
The substrate on which hard bias layers are formed in some head designs is NiO or alumina. Rhodium has been used as a lead material for these heads. Other designs use PtMn as the substrate for the hard bias layer on which the leads must be formed. However, the resistance of rhodium leads is unacceptably increased when the hard bias and lead stack are formed on a PtMn substrate.